The present invention relates generally to the field of power line carrier systems and high-voltage electric power transmission line protection. Power line carrier systems are used by electric utilities in high-speed protection schemes for electrical faults occurring on high-voltage transmission lines. Line traps, which may also be known as wave traps, are an integral part of these power line carrier systems. Line traps are basically band-reject or notch filters composed of resistive, inductive, and capacitive components. As such, line traps must be tested regularly to ensure proper tuning for overall system performance. In other words, the blocking characteristics of the line trap must be measured periodically to verify that the electrical components comprising the line trap are tuned to block, or trap, the desired power line carrier signal frequency or band of frequencies used in a particular power line carrier installation.
Because a line trap is energized at the same electrical potential as the transmission line to which it is connected, heretofore it has been known that methods for directly measuring the blocking characteristics of a line trap required the line trap to be de-energized and grounded to earth potential so that test equipment could be connected to the line trap. Hence, the high-voltage transmission line to which the line trap is connected must also be de-energized and grounded to earth potential. Electric utilities can incur significant monetary and reliability expenses when they take a high-voltage transmission line out of service. A primary economic advantage gained is in time and manpower. There is significant time and manpower involved in taking a transmission line out of service to test a line trap. Additionally, reliability of the transmission system is at risk anytime a major power flow corridor (a high-voltage transmission line) is out of service. If another transmission line were to be unexpectedly taken out of service by some abnormal system condition, overall system stability can be jeopardized. Furthermore, there is the risk of human error or equipment malfunction during the process of taking a line out of service that could result in significant loss of load, which equates to lost revenue for an electric utility. Therefore, a method for determining the blocking characteristics of a line trap without de-energizing the line trap would be highly beneficial to the electric utility industry for both economic and reliability reasons.